Abiogenesis
(pronounced /ˌeɪbaɪ.ɵˈdʒɛnɨsɪs/ ay-by-oh-jen-ə-siss) or biopoesis is the study of how biological life arises from inorganic matter through natural processes, and the method by which life on Earth arose. Most amino acids, often called "the building blocks of life", can form via natural chemical reactions unrelated to life, as demonstrated in the Miller–Urey experiment and similar experiments that involved simulating some of the hypothetical conditions of the early Earth in a laboratory.In all living things, these amino acids are organized into proteins, and the construction of these proteins is mediated by nucleic acids, that are themselves synthesized through biochemical pathways catalysed by proteins. Which of these organic molecules first arose and how they formed the first life is the focus of abiogenesis.
In any theory of abiogenesis, two aspects of life have to be accounted for: replication and metabolism. The question of which came first gave rise to different types of theories. In the beginning, metabolism-first theories (Oparin coacervate) were proposed, and only later thinking gave rise to the modern, replication-first approach.
The first living things on Earth are thought to be single cell prokaryotes (which lack a cell nucleus), perhaps evolved from protobionts (organic molecules surrounded by a membrane-like structure).The oldest ancient fossil microbe-like objects are dated to be 3.5 Ga (billion years old), approximately one billion years after the formation of the Earth itself, with reliable fossil evidence of the first life found in rocks 3.4 Gyr old. By 2.4 Ga, the ratio of stable isotopes of carbon, iron and sulfur shows the action of living things on inorganic minerals and sediments and molecular biomarkers indicate photosynthesis, demonstrating that life on Earth was widespread by this time.
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